A rotor or stator blade for a compressor or a gas turbine has a convex outer surface or suction side and a concave inner surface or pressure side, which are joined at their upstream ends by a leading edge and at their downstream ends by a trailing edge for the gases. The pressure side and the suction side are attached to a platform, which is provided with a blade root of the dovetail, fir-tree or similar type, intended to be inserted into a corresponding cavity in a rotor disc of the compressor or the gas turbine.
A lateral reinforcing web called a “stiffener” is formed beneath the platform, between an inner surface of the latter and a lateral surface of the blade root, and extends transversely beneath a downstream part of the platform. If necessary, another stiffener is also formed beneath an upstream part of the platform.
These stiffeners serve also as support for a sealing skirt placed between two adjacent blades in order to prevent flow of air from the internal part of the turbine radially towards the pressure and suction sides of the blades and, conversely, to prevent flow of gas or air from the pressure and suction sides of the blades as far as the internal part of the gas turbine. The cool air from the internal part can thus enter air intake orifices provided at the end of the blade roots and supplying a network of ventilation ducts formed on the inside of the blades, in order to cool them.
When the compressor or turbine is in operation, the pressure and suction sides of the blades, which are subjected to centrifugal forces, have a tendency to move radially outwards. The centrifugal forces therefore generate large forces in the joint region between the blade aerofoil and the platform, and create high stresses in this joint region and more particularly in the joint between the blade trailing edge and the platform.
These stresses are liable to weaken the blades and reduce their lifetime.
The object of the invention is in particular to provide a simple, inexpensive and effective solution to this problem.
The subject of the invention is a compressor or gas turbine blade in which the loads applied by the centrifugal forces to the joint region between the aerofoil and the platform of the blade are limited.